We hypothesize that there is a correlation between the administration of Gd-containing agents usually associated with MRI procedures and the development of NSF in those with renal failure and some other predisposing condition. We also hypothesize that tissue Gd levels in those with NSF will be higher than in those who have been exposed to GBCA but do not have NSF. Of the two groups without NSF but with exposure to GBCA, we hypothesize that those with kidney dysfunction will have higher tissue Gd levels than those with normal kidney function. We hypothesize that in the two groups of subjects without exposure to GBCA, there will be no detectable levels of Gd, regardless of kidney function status.